Preyssler-type Polyoxometalate Research Articles

A facile strategy for the preparation of monatomic silver

The surface free energy of metal increases with the decrease of the metal particle sizes, which contributes to the aggregation of isolated single atoms into nanoparticles during synthesis and reaction processes. The common disadvantages of traditional methods for preparing monatomic catalysts are low loading capacity, easy aggregation of atoms and complex preparation methods. These disadvantages limit the application of monatomic catalysts. In this paper, a simple, stable and repeatable method for preparing monatomic silver catalyst without high temperature is explored. Preyssler-type polyoxometalate is a metal oxide with a cavity disk structure, and Na+ in the cavity structure can be replaced by Ag+ by hydrothermal method. Under the action of reducing agent, Ag+-containing polyoxometalate can be converted into monatomic silver, and under the protection of surfactant, monatomic silver can be stably maintained for one month.

Effect of Nonconstituent Additive Ions on the Controlled Crystallization of Lanthanide-Based Preyssler Polyoxometalates.

Preyssler-type polyoxometalates (POMs) encapsulating lanthanide ions have been shown to provide ideal examples of single-molecule magnets and spin-qubits. However, the advances in this area are limited by the quality and size of the crystals. In this work, the role of additives ions in the crystallization of these POMs from aqueous solutions has been investigated. More specifically, we have studied the influence of Al3+, Y3+, and In3+ on the crystallization process of K12[MP5W30O110] (where M = Gd and Y). The results show that the concentration of these ions in the solution plays an important role in controlling the crystallization rate of the grown POM crystals leading to a significant increase in their size, while showing very little or no tendency to be incorporated into the structure. This has allowed us to obtain pure Gd or Y crystals, as well as diluted magnetic crystals formed by the diamagnetic Y3+ POM doped with the magnetic Gd3+ ion.

Experimental observation of the role of countercations in modulating the electrical conductance of Preyssler-type polyoxometalate nanodevices.

Polyoxometalates are nanoscale molecular oxides with promising properties that are currently explored for molecule-based memory devices. In this work, we synthesize a series of Preyssler polyoxometalates (POMs), [Na⊂P5W30O110]14-, stabilized with four different counterions, H+, K+, NH4+, and tetrabutylammonium (TBA+). We study the electron transport properties at the nanoscale (conductive atomic force microscopy, C-AFM) of molecular junctions formed by self-assembled monolayers (SAMs) of POMs electrostatically deposited on the ultraflat gold surface prefunctionalized with a positively charged SAM of amine-terminated alkylthiol chains. We report that the electron transport properties of P5W30-based molecular junctions depend on the nature of the counterions; the low-bias current (in the voltage range [-0.6 V; 0.6 V]) gradually increases by a factor of ∼100 by changing the counterion in the order: K+, NH4+, H+ and TBA+. From a statistical study (hundreds of current-voltage traces) using a simple analytical model for charge transport in nanoscale devices, we show that the energy position of the lowest unoccupied molecular orbital (LUMO) of P5W30 with respect to the Fermi energy of the electrodes increases from ∼0.4 eV to ∼0.7 eV and that the electrode coupling energy also increases from ∼0.05 to 1 meV in the same order from K+, NH4+, H+ to TBA+. We discuss several hypotheses on the possible origin of these features, such as a counterion-dependent dipole at the POM/electrode interface and counterion-modulated molecule/electrode hybridization, with, in both cases, the largest effect in the case of TBA+ counterions.

Efficient Electrochemical Detection of Hydrogen Peroxide Based on Silver-Centered Preyssler-Type Polyoxometalate Hybrids.

Four polyoxometalate (POM)-based organic-inorganic hybrid compounds, namely, (H2bimb)6H8[((Mn(H2O)3(μ-bimb))0.5(Mn(H2O)4)(Mn(H2O)5)0.5(AgP5W30O110))2]·29H2O (1), [(Cu(Hbimb)(H2O)2(μ-bimb)Cu(Hbimb)(H2O))(Cu(H2O)2(μ-bimb)Cu(H2O)3)((Cu(H2O)2)0.5(μ-bimb)(Cu(H2O)3)0.5)H2(AgP5W30O110)]·12.5H2O (2), (H2bimb)2H[(Zn(Hbimb)(H2O)4(Zn(Hbimb)(H2O)2)0.5)2(AgP5W30O110)]·12H2O (3), and (H2bimb)3H2[(Ag(H2O)2)0.5(Ag(Hbimb)Ag(Hbimb)(μ-bimb)Ag)(Ag(H2O)2)0.5(AgP5W30O110)]·7H2O (4) (bimb = 1,4-bis(1H-imidazol-1-yl)benzene), were hydrothermally synthesized using a silver-centered Preyssler-type POM K14[AgP5W30O110]·18H2O (abbreviated as K-{AgP5W30}) as a precursor. In 1-4, {AgP5W30} clusters integrating the merits of Ag+ and {P5W30} units are modified by different transition metal (TM)-organic fragments to extend the structures into three-dimensional frameworks. As nonenzymatic electrochemical sensor materials, 1-4 show good electrocatalytic activity, high sensitivity, and a low detection limit for detecting hydrogen peroxide (H2O2); 4 possesses the highest sensitivity of 195.47 μA·mM-1·cm-2 for H2O2 detection. Most importantly, the average level of H2O2 detection of these {AgP5W30}-based materials outperforms that of Na-centered Preyssler-type {NaP5W30} and most Keggin-type POM-based materials. The performances of such {AgP5W30} materials mainly stem from the unique advantage of high-negatively charged {AgP5W30} clusters together with the good synergistic effect between {AgP5W30} and TMs. This work expands on the research of high-efficiency POM-based nonenzymatic electrochemical H2O2 sensors using Ag-containing POMs with high negative charges, which is also of great theoretical and practical significance to carry out health monitoring and environmental analysis.

Enhanced dual-band modulation of visible and near-infrared light transmittance in electrochromic composite films based on Preyssler-type polyoxometalates and W18O49

Benefitting from a unique wrap-type porous nano-structure, a POM/W18O49 composite film achieved excellent electrochromic properties and a high coloration efficiency, and is promising for applications in smart windows.

Ultrahigh Proton Conduction via Extended Hydrogen-Bonding Network in a Preyssler-Type Polyoxometalate-Based Framework Functionalized with a Lanthanide Ion.

The exploration of composition-structure-function relationship in proton-conducting solids remains a challenge in materials chemistry. Polyoxometalate-based compounds have been long considered as candidates for proton conductors; however, their low structural stability and a large decrease in conductivity under reduced relative humidity (RH) have limited their applications. To overcome such limitations, the hybridization of polyoxometalates with proton-conducting polymers has emerged as a promising method. Besides, 4f lanthanide ions possess a high coordination number, which can be utilized to attract water molecules and to build robust frameworks. Herein, a Preyssler-type polyoxometalate functionalized with a 9-coordinate Eu3+ (Eu[P5W30O110K]11-) is newly synthesized and combined with poly(allylamine) with amine moieties as protonation sites. The resulting robust crystalline composite exhibits an ultrahigh proton conductivity >10-2 S cm-1 at 368 K and 90% RH, which is still >10-3 S cm-1 at 50% RH, due to the strengthened and extended hydrogen-bonding network.

Bacterial hyperpolarization modulated by polyoxometalates for solutions of antibiotic resistance

Developing strategies against the antibiotic resistance is a major global challenge for public health. Here, we report the synergy of the combination of Preyssler-type polyoxometalates (POMs) ([NaP5W30O110]14− or [AgP5W30O110]14−) and ribosome-targeting antibiotics for high antibacterial efficiency with low risk of antibiotic resistance. Due to their ultra-small sizes and active surface ligands, POM anions show strong affinity to bacterial cell membrane and impose hyperpolarization of the bacterial cells as well as the decrease of Mg2+ influx by blocking Mg2+ transporters, which finally lead to the structural perturbations of ribosomes and instability of bacterial structures. The bacterial growth can, therefore, be regulated by the presence of POMs: a fraction of Bacillus subtilis shifted to a ‘dormant’, slow-growing cellular state (an extended lag phase) upon the application of subinhibitory concentration of POMs. An approach to combat antibiotic resistant bacteria by applying POMs at their early growth phase followed by antibiotic exposure is validated, and its high efficiency for bacterial control is confirmed.

Density functional theory study of single-molecule ferroelectricity in Preyssler-type polyoxometalates

A detailed study on the single-molecule ferroelectric property of Preyssler-type polyoxometalates (POMs), [M3+P5W30O110]12− (M = La, Gd, and Lu), is performed by density functional theory calculations. Linked to one H2O molecule, the cation (M3+) encapsulated in the cavity of the Preyssler framework is off-centered, and it generates a permanent dipole, which is essential for a ferroelectric ground state. Accompanied with a 180° rotation of H2O, the switching of M3+ between two isoenergetic sites on both sides of the cavity results in a calculated barrier of 1.15 eV for Gd3+, leading to the inversion of electric polarization. The height of the barrier is in good agreement with the experimentally measured barrier for the Tb3+ ion, whose ionic radius is similar to Gd3+. The total polarization value of the crystal is estimated to be 4.7 µC/cm2 as calculated by the modern theory of polarization, which is quite close to the experimental value. Considering that the order of contributions to the polarization is M3+–H2O > counter-cations (K+) > [P5W30O110]15−, the interconversion of M3+–H2O between the two isoenergetic sites is predicted to be the main origin of ferroelectricity with a polarization contribution of 3.4 µC/cm2; the K+ counter-cations contribute by 1.2 µC/cm2 and it cannot be disregarded, while the framework appears to contribute negligibly to the total polarization. Our study suggests that a suitable choice of M3+–H2O could be used to tune the single-molecule ferroelectricity in Preyssler-type polyoxometalates.

Enhanced Electrochromic Performance of Film Based on Preyssler-Type Polyoxometalate and Tungsten Oxide

Tungsten oxide (WO3) has received attention as an electrochromic material because of its excellent properties. However, the long switch time and low coloration efficiency of WO3 film limit its use. Herein, a nanocomposite film containing Preyssler-type polyoxometalate (POM) K12.5Na1.5[NaP5W30O110]·15H2O (P5W30) and WO3 nanoparticles has been fabricated by layer-by-layer (LbL) self-assembly methods and characterized by UV-Vis spectra, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical workstation. Compared to the pure WO3 film, the [P5W30/WO3]20 film has better electrochromic properties. Then, the electrochromic properties of [P5W30/WO3]20 film were studied in different electrolyte. The results indicated that the composite film show high coloration efficiency (191.62 cm2 C− 1), fast switch time (2.58 s, 1.48 s), good CV stability (500 th) in 0.5 M LiClO4/PC electrolyte, and successfully assembled of an electrochromic device. These advantages can make the nanocomposite film become a promising candidate for potential application in electrochromic devices.

P5W30/g-C3N4heterojunction thin film with improved photoelectrochemical performance for solar water splitting

For the first time, to design a new photocatalyst, a Preyssler-type polyoxometalate was composited with g-C3N4to improve its photoelectrochemical performance.

Effect of molecular weights of confined single-chain poly(allylamine) toward proton conduction in inorganic frameworks based on Preyssler-type polyoxometalate

In this work, poly(allylamine) (PAA) of different average molecular weights (MW = 1600 (I), 3000 (II), and 5000 (III)) are confined in an inorganic framework composed of K+ and Preyssler-type polyoxometalate [Na(H2O)P5W30O110]14−, and the effects toward proton conduction are investigated. All compounds possess one-dimensional channels with a minimum aperture of ca. 6 Å, where water molecules and PAA reside. Proton conductivities at 348 K, RH 75% are 2.1–3.5 × 10−3 S cm−1 and in the same range, while activation energies of the proton conductions are I (0.46 eV) > II (0.33 eV) ≃ III (0.29 eV) and quite large for I. Relaxation times estimated from 13C-CPMASNMR show that the mobility of the PAA backbone is I < II ≃ III, suggesting that PAA with a low molecular weight is anchored in the inorganic framework. On the other hand, the mobility of the PAA sidechain is I > II ≃ III. Considering the large activation energy of I and that protonated amine group resides on the sidechain of PAA, sidechain mobility of PAA is crucial to the proton conduction in I, while those in II and III occur via rearrangement of hydrogen-bonding networks composed of water molecules and PAA.

Self-assembly of m-phenylenediamine and polyoxometalate into hollow-sphere and core-in-hollow-shell nanostructures for selective adsorption of dyes

Supramolecular self-assembly is an effective method to assemble organic and inorganic units into various hierarchical structures with excellent properties and is widely used in material and life science. In this article, the self-assembled hollow-sphere and core-in-hollow-shell nanostructures composed of m-phenylenediamine and a novel Preyssler-type polyoxometalates (POM, K12.5Na1.5[NaP5W30O110]·15H2O (abbreviated as P5W30)) without template were successfully realized by adjusting the non-covalent interactions. For comparison, we also selected o-phenylenediamine and p-phenylenediamine to investigate whether isomerides have different effects on the self-assembly behavior with P5W30. The results indicated that only m-phenylenediamine/P5W30 can form hollow spheres and core-in-hollow-shell structure while o-phenylenediamine/P5W30 and p-phenylenediamine/P5W30 cannot which revealed that the self-assembly process can be regulated via isomer effects. Moreover, the detailed analysis of the formation of hollow spheres and core-in-hollow-shell structure are studied and the mechanism is mainly due to the Ostwald ripening. In addition, m-phenylenediamine/P5W30 composite has a good adsorption capacity for methylene blue (MB) dyes, even in the presence of other dyes such as rhodamine B (RB) and amaranth (AR). Our findings further confirmed that supramolecular self-assembly between organic molecules and POM can unique a distinctive “bottom-up” strategy to construct diversiform structures with functional properties.

A Preyssler-type polyoxometalate-based coordination supramolecule with proton conducting property

Developing new low-cost and efficient proton-conducting materials remains an attractive and challenging task. Herein, a Preyssler-type polyoxometalate derived coordination compound had been synthesized with a hydrothermal method, namely, H4.5NaCo5(2-MI)15.5(2-MI)3 [NaP5W30O110]·5H2O (1) (where 2-methylimidazole is abbreviated as 2-MI, and partial 2-MI was deprotonated). The structure was characterized by single crystal X-ray diffraction, PXRD, FT-IR, TG, CHN and ICP-OES elemental analyses. We studied the relationship between the crystal structure and proton conduction of compound 1 and found that the presence of 2-MI reduced the leakage of polyoxometalate under high relative humidity. Meanwhile, the strong interaction of the counter cation Na+ with water is beneficial to form more hydrogen bonds. Compound 1 showed the maximum proton conductivity with a value of 4.42 × 10−3 S cm−1 at 367 K and 97% RH. Kinetic investigation indicates that the proton conduction mechanism of compound 1 follows the vehicle mechanism.

Confinement of poly(allylamine) in Preyssler-type polyoxometalate and potassium ion framework for enhanced proton conductivity

Polyoxometalate based solids are promising candidates of proton-conducting solid electrolytes. In this work, a Preyssler-type polyoxometalate is crystallized with potassium ions and poly(allylamine), which is also a good proton conductor, from aqueous solutions. Here we show that the hygroscopicity induced low durability of polyoxometalate and poly(allylamine) can be circumvented by the electrostatic interaction between the polyoxometalate and protonated amine moieties in the solid state. Crystalline compounds are synthesized with poly(allylamine) of different average molecular weights, and all compounds achieve proton conductivities of 10−2 S cm−1 under mild-humidity and low-temperature conditions. Spectroscopic studies reveal that the side-chain mobility of poly(allylamine) and hydrogen-bonding network rearrangement contribute to the proton conduction of compounds with poly(allylamine) of low and high average molecular weights, respectively. While numbers of proton-conducting amorphous polyoxometalate-polymer composites are reported previously, these results show both structure-property relationship and high functionality in crystalline composites.

Preyssler‐based nanocomposite as a magnetic photocatalyst: synthesis, characterisation and its photocatalytic activity for decolourisation of rhodamine B

In this work, the authors prepared a novel magnetic photocatalyst by grafting of Preyssler-type polyoxometalate, H 14 [NaP 5 W 30 O 110 ] onto Fe 3 O 4 nanoparticles via an internal layer of silver nanoparticles. The obtained nanocomposite has been characterised by electron dispersive X-ray, transmission electron microscopy and scanning electron microscopy. The activity of the synthesised nanomagnetic photocatalyst was tested by the photocatalytic decolourisation of rhodamine B under UV light irradiation in the study's designed reactor. It was found that, compared to pure Preyssler, decolourisation of rhodamine B was occurred four times faster using the synthesised magnetic nanocomposite with easy separation. The magnetic nanocatalyst was separated after ending the reaction and recycled. It just showed 2-3% decrease in catalytic activity after four recycling.

Enhanced electrochromic performance of nanocomposite film based on Preyssler-type polyoxometalate and TiO2 nanowires

A nanocomposite film containing Preyssler-type polyoxometalate (POM) K12.5Na1.5[NaP5W30O110] (P5W30) and TiO2 nanowire arrays was fabricated by combining hydrothermal and Layer-by-Layer (LbL) self-assembly methods. Compared to individual TiO2 nanowire and P5W30 thin film, the composite films exhibits improved electrochromic properties of higher optical modulation (46.03% at 650 nm), faster switching times (7.03 s for coloration and 2.55 s for bleaching), outstanding coloration efficiency (163.4 cm2/C at 650 nm) and good cycling stability. Obviously, the enhancement of electrochromic performances can be attributed to the synergetic contribution from P5W30 and TiO2, which displays large real active area to support larger Li+ ion insertion and extraction sites. These advantages can make the nanocomposite film become a promising candidate for potential application in electrochromic devices.

Giant Hysteretic Single-Molecule Electric Polarisation Switching above Room Temperature.

Continual progress has been achieved in information technology through unrelenting miniaturisation of the single memory bit in integrated ferromagnetic, ferroelectric, optical, and related circuits. However, as miniaturisation approaches its theoretical limit, new memory materials are being sought. Herein, we report a unique material exhibiting single-molecule electric polarisation switching that can operate above room temperature. The phenomenon occurs in a Preyssler-type polyoxometalate (POM) cluster we call a single-molecule electret (SME). It exhibits all the characteristics of ferroelectricity but without long-range dipole ordering. The SME affords bi-stability as a result of the two potential positions of localisation of a Tb3+ ion trapped in the POM, resulting in extremely slow relaxation of the polarisation and electric hysteresis with high spontaneous polarisation and coercive electric fields. Our findings suggest that SMEs can potentially be applied to ultrahigh-density memory and other molecular-level electronic devices operating above room temperature.

Giant Hysteretic Single‐Molecule Electric Polarisation Switching above Room Temperature

AbstractContinual progress has been achieved in information technology through unrelenting miniaturisation of the single memory bit in integrated ferromagnetic, ferroelectric, optical, and related circuits. However, as miniaturisation approaches its theoretical limit, new memory materials are being sought. Herein, we report a unique material exhibiting single‐molecule electric polarisation switching that can operate above room temperature. The phenomenon occurs in a Preyssler‐type polyoxometalate (POM) cluster we call a single‐molecule electret (SME). It exhibits all the characteristics of ferroelectricity but without long‐range dipole ordering. The SME affords bi‐stability as a result of the two potential positions of localisation of a Tb3+ ion trapped in the POM, resulting in extremely slow relaxation of the polarisation and electric hysteresis with high spontaneous polarisation and coercive electric fields. Our findings suggest that SMEs can potentially be applied to ultrahigh‐density memory and other molecular‐level electronic devices operating above room temperature.

Photovoltaic properties of supramolecular assemblies obtained by incorporation of Preysler's type polyoxometalate in a polycationic copolymer of porphyrin

Poly-zinc-octaethylporphyrin/P5W30 films have been obtained through incorporation of Preyssler-type polyoxometalate ions, namely [NaP5W30O110]14- (P5W30) into zinc octaethylporphyrin/viologen-based polymers (poly-ZnOEP) films. The latter has been achieved through a metathesis reaction involving exchange of the initial counter ions (PF6−) of the positively charged poly-ZnOEP by P5W30. The investigated polymers involve ZnOEP units covalently linked either through a dicationic mono-viologen or through a tetracationic bis-viologen spacer. These copolymers have been characterized by UV/Vis absorption spectroscopy, X-ray photoelectron spectroscopy, electrochemistry, AFM and by electrochemical impedance spectroscopy. Formation of the polymers through electropolymerization of viologen and porphyrin building blocks has also been monitored by EQCM. QCM measurements have been carried out to study the exchange of PF6− by [NaP5W30O110]14−. Finally, the photovoltaic performances of these polymers have been assessed by photocurrent transient measurements carried out under visible illumination.

Extended structural materials constructed from sulfate-centered Preyssler-type polyoxometalate with excellent electrocatalytic property

Sulfate-centered Preyssler-type polyoxometalate was used as the precursor to react with transition metal cations and organic ligand for constructing inorganic-organic hybrid materials {H[Ni2(H2O)4(Htrz)3]2(KS5W30O110)}∙18H2O (trz=1,2,4-triazole) (1), which was characterized by single crystal X-ray diffraction analysis, energy-dispersive X-ray (EDX), power X-ray diffraction (PXRD), IR spectra and thermogravimetric (TG) analyses. In 1, the cylindrical vacancy of the inorganic crown-type anion {S5W30O110} captures a K+ ion resulting in the anion {KS5W30O110}9−, which was further connected by dimeric [Ni2(H2O)4(Htrz)3]2 metal-organic units into an one-dimensional (1D) chain-like structure. These 1D chains are further packed to form a three-dimensional (3D) supramolecular structure via H-bonding interactions. Here, the sulfate-centered Preyssler-typepolyoxometalate was firstly used to coordinate with transition metal cations and introduced into the inorganic-organic hybrid materials. Electrocatalytic study indicates that compound 1 exhibits good electrocatalytic activity toward reduction of H2O2 and NO2−.